Method for preparing vanadate phosphors



United States Patent 3,424,692 METHOD FOR PREPARING VANADATE PHOSPHORSSam Z. Toma, Towanda, James E. Mathers, Ulster, and

Felix F. Mikus, Towanda, Pa., assignors to Sylvania Electric ProductsInc., a corporation of Delaware No Drawing. Filed Apr. 22, 1966, Ser.No. 544,390 US. Cl. 252-301.4 5 Claims Int. Cl. C09k 1/44 ABSTRACT OFTHE DISCLOSURE The particle size of a vanadate phosphor can becontrolled by adding potassium cations to the blend of raw materialsused to make up the phosphor.

This invention relates to a method of producing improved yttrium and/ orgadolinium vanadate phosphors. More specifically, this invention relatesto a method of preparing such phosphors wherein the particle size iscontrolled within desired parameters.

Yttrium and gadolinium vanadadate phosphors are known to the art andmethods have previously been developed for their production. Today, theyfind their greatest applicability in cathode-ray tubes as a red-emittingcomponent of a three color screen. In the manufacture of the phosphorscreens, great care must be taken to control the particle sizes of thephosphor. Manufacturing techniques commonly used require a narrow sizedistribution of the particles and unless this narrow spread is attained,the screen will not operate at maximum efficiency.

To obtain particles of a desired size, the art generally ball milled thephosphors for extended periods of time in order to reduce any largeparticles to within usable limits. But ball milling reduces the particlesize of all particles indiscriminately. Large particles were broken intosmaller ones, but those which already have small sizes were reduced intofines. Large quantities of fines in the phosphor can be highlydisadvantageous. On the other hand, it is possible to remove the largeparticles and fines by techniques such as elutriation, but theseprocesses tend to be rather expensive and wasteful. Hence, it isdesirable to produce a phosphor in specific particle size ranges byprocessing techniques, so that operations such as ball milling and/orelutriation steps can be eliminated.

To this end, we have discovered that the addition of potassium cationsto the yttrium and/or gadolinium vanadate phosphor-forming raw materialmixture will decrease the particle size to a desired extent. Moreover,such additions do not effect the efiiciency of the phosphor when addedin controlled quantities and in some cases may even enhance body color.After firing, the potassium cations are washed out of the phosphor.

The primary object of our invention is to produce yttrium and gadoliniumvanadate phosphors in a desired particle size range withoutsubstantially changing the efliciency of the phosphor.

A feature of our invention is the addition of potassium cations incontrolled quantities to a yttrium and/or gadolinium vanadate phosphorforming raw material formulation.

The many other objects, features and advantages of our invention willbecome manifest to those conversant with the art upon reading thefollowing specification.

According to our invention, the raw materials necessary-to formulate ayttrium and gadolinium vanadate phosphor are mixed together and 0.01 to0.50 mole percent of potassium cation are added per mole of YVO Theparticular anion which is added seems to have little or no effect uponthe overall process. The nitrate, nitrite,

3,424,692 Patented Jan. 28, 1969 perchlorate, chlorate, chloride,silicate, oxalate, hydroxide, carbonate, phthalate and vanadate ofpotassium give substantially similar results. Table I, following, showshow the particle size of the phosphor is reduced when quantities ofpotassium flux are added to the raw material blend. In each case, as theamount of potassium is increased, the particle size is reduced. However,the potassium concentration must not be so great as to reduceappreciably the brightness of the phosphor and hence, must be in thedescribed ranges. The particles will be less than 8 microns.

TABLE I Percent K wt. Mole K/mole YVO4 F888 As indicated in Table II,the particle size of the phosphor will decrease irrespective of thepotassium anion which is used.

TABLE II Percent K Wt. added Salt added KNO3 Particle size FSSS KNOgKVOa

Without limiting this invention the following specific examples areoffered as a method of preparing the phosphor.

Example I Intimately mix the following raw material components includingthe potassium cation by the usual blending operations such as rolling,tumbling or milling. The phosphor is efiectively developed by firing thecomponents in a shallow silica tray at conventional temperatures. Afterfiring the phosphor is washed to remove the potassium cations.

Materials: Weight, grams Y (C O 2713.5 Eu (C O NH VO 2810.0 KCIO, 46.9

This method gives both particle size control and narrows particledistribution. The number of oversized and undersized particles issubstantially decreased, hence elimination of these results andsubstantial processing enables the production of a good cathode ray tubescreen with a smaller amount of phosphor per unit area.

Example II yttrium, vanadium, europi-um compound precipitates out and isfired to produce yttrium vanadate activated by europium. The phosphor iswashed to remove the potassium cations.

It is apparent that modifications and changes may be made within thespirit and scope of the invention, but it is our intention however onlyto be limited by the scope of the appended claims.

As our invention, we claim:

1. In the process for manufacturing a vanadate phosphor, the steps whichcomprise: mixing together raw materials necessary to form said vanadatephosphor, and adding thereto a potassium cation; firing the mixture andrecovering a vanadate phosphor; Washing said vanadate phosphor to removethe potassium cations and recovering a phosphor having a particle sizeless than about 8 microns.

2. The process according to claim 1 wherein the vanadate phosphor is atleast one member selected from the group consisting of yttrium andgadolinium.

References Cited UNITED STATES PATENTS 3,152,085 10/1964 Ballman et a1252301.4 3,357,925 12/1967 Levine et a1 252-30l.4 3,380,926 4/1968Harper 252301.4

TOBIAS E. LEVOW, Primary Examiner.

ROBERT D. EDMONDS, Assistant Examiner.

